Ventilation System Troubles

Sounds like you're on the right track. I'd start by looking for a vacuum leak in the supply line from the engine to the control panel. Possibly a bad vacuum cannister somewhere under the hood.

I was hoping for more hand holding than that. I can't find anything, and I have looked. What I need to know is how the system even works... If I was going to devise a life support system, I'd not make it dependent on vacuum. All I can think of is that they want the AC to drop offline during heavy loads where regaining the 3 or 4 HP that the AC consumes would be useful, but beyond that I see no reason to peg life support to vacuum loads on the engine.

You don't remember the old vacuum wipers? When the vacuum would go away they quit working. Now, *those* were the good ol' days. The HVAC system generally defaults to the Defrost setting when the vacuum goes away. Not sure of the why, just that it does(spring loaded actuators and such). I guess somewhere's gotta be the "home" position for all those doors so they picked Defrost. Maybe so the system can allow slight airflow over the windshield even when it's in the Off position to keep the window clear? Somewhere under the hood there should be a vacuum reservoir that looks like either a ball or a black coffee can. Should be one or two vac. hoses connected to this reservoir. Usually, when th HVAC starts behaving as yours, this tank(or associated hoses)has sprung a leak.

Jeff, If your local library has a decent reference section, you might find a vacuum diagram in a Chilton's or Ford manual.

It looks like the vacuum canister is above the right wheel well (according to my '96 truck manual). From there, the line goes to a check valve with two outlets, kind of "F" shaped. That check valve may be under the hood, or in the passenger compartment. I would start at the canister and try to follow the line from there. On older vehicles, it may not only be the hoses that harden and crack, but also the fittings, especially here in the south. The heat is hell on them.

I remember the vacuum wipers- what a PITA they were!

-- SC Tom

Loss of vacuum results in the HVAC system going to default settings (for safety reasons) which are defrost mode.

I'd suspect a combination of a possible restriction, along with a vacuum leak is what's up. The ECM covers up the vacuum leak, adjusting mixture so it doesn't run too lean, but can't fix up the HVAC.

Check the HVAC vacuum lines, especially any connectors that are rubber, as they split frequently.

Hey, quit brining up bad memories of heading up a steep hill, and having no wipers. You could not let off the gas to get vacuum and make the hill, so the alternative was to open a window and stick one's head out!

Ah, yes, remember those good old days very well...

I would definitely check out the vacuum check valve, a plastic disk in the line from the engine manifold. If it fails, then the vacuum drops to less than 2", as when under hard acceleration, the vents all return to their default spring loaded position.

A leak would be a constant failure, whereas a bad check valve would cause this trouble you described.

Well, speaking of Vacuum and problems associated with them (I remember Dad had a '56 Ford, and driving on what they used to have instead of freeways then was bad. If you kept up, the wipers slowed down so much as to be useless.. But everyone was in the same boat then, so who knew any better?) , I have another vacuum question.

The Edsel got a lot of noise about why it failed, but I had a mechanic type who told me that the controls were highly vacuum and therefore prone to all the problems that we all remember. THAT was why the thing failed to sell as it might have, and that is why the thing is in the "Missed it by THAT much" category when talking about successful merchandising.

So is there anyone here who might remember or know about this?

On Mon, 31 Jan 2011 16:57:36 -0700, Sebastian Tombs rearranged some electrons to say:

Vacuum controls were (and still are) common. The Edsel was a butt-ugly car, and it competed directly with Ford's other more well known brands, specifically Mercury. Although he wasn't responsible for the car, Robert McNamara essentially killed it off.

The 58 Edsel that I owned the controls (HVAC, transmission) both were electrical, not vacuum. The HVAC system was an amazing device with a cam disk that moved about eight cables for the various doors. The transmission controller was similar but not a cam disk--very similar to the present day transfer case controllers.

Both of these were so prone to failure that it was not uncommon to see Edsel owners crawling under the car to wiggle the transmission controller's output arm to get it to move. The HVAC one used a big printed circuit to define where it was supposed to stop, and the contact would get dirty resulting is the HVAC system simply stopping whereever it wanted.

IMHO it failed for a lot of reasons, wrong product at the wrong time (expensive car in a post war depression time, lack of quality control led to many unhappy owners, and a few other problems.) The first 58 Edesl vehicles were essentially hand built BTW, and it showed!

(Above!)

I had a 1959 Edsel Convertible for many years (1964-1980) and loved it. Only sold it because I was moving cross country. I never had any problems with it. They changed a lot of things (like the transmission controls) that year.

Glen

Interesting. So it sounds like maybe a little too much cutting edge technology with a little too little testing before selling?

I personally never thought it was all THAT butt-ugly (detroit foisted a lot of uglier sisters onto the public that moved and succeeded), but his is an interesting perspective.

Thanks for the reply.

S.

I've been working in a resto/hot rod shop for like 5 years, and I have yet to see one come in. I always kinda liked the Edsel's look, but then I'm probably not a good judge...I had a '73 Gremlin that I absolutley loved.

I don't know if your 97 has the fresh air door solenoid in the engine compartment or not but, if so, look for a white

3/32" vacuum tube going to the vacuum motor that operates it. Not being a chemist, I cannt tell you why, but, exposure to the elements under the hood cause it to become porous allowing leakage right thru the tube itself. It is usually stiff, brittle and easily broken in the advanced stage of detrerioration. You can replace the exposed section with vacuum hose or, replace the entire tube all the way into the cab. I have not seen any benefit to being that gungho about repairing it.

As far as gaining a bit of horsepower, many fords have a wide open throttle cutout feature for the a/c compressor clutch that releases the clutch above about 3/4 throttle until about 10 seconds after the load has been removed. It is usually controlled by the ECM and a relay. Some older vehicles had a similar setup using a vacuum switch to sense engine load. I installed a vacuum system on my old 72 351CJ because it kept eating compressors after using passing gear a few times. Seems the compressor was not capable of living very long at 6K+ RPM. Yours very likely has the ECM controlled WOT compressor cutout.

Lugnut

That is great info, and a second possible reason, but, he said it recently started doing the defroster on WOT. There is good merit in what you state. Thanks.

The trouble is that he loses vacuum at WOT, and default settings bring the vacuum motors to their at-rest condition, which directs the blower to defrost the windshield. Does this also occur when the compressor WOT circuit cuts in?

If so, your info is another possibility, after he checks out the vacuum check valve to assure it is not defective.

I hope all of our input helps! And, would like to know the solution he finds!

Sorry for my confusion, but at Wide Open Throttle, the system does it's job properly. I think. I don't do WOT as a general rule, so I can't say with any certainty that this is an indicator. I think that when the engine is screaming along at the upper limits of the tach, the vent system does what I have set the dials for.

The trouble is at cruise speeds of about 1500 to 200 RPMs, any light increase in speed causes the life support system to clam up. If I shift out of OD (press the button or move the shifte lever) at the same speed, and force the engine to jump to 3000 RPMs, then the life support system comes back.

So, I cruise on the freeway at 65-ish and something like 2000 RPM, and all is good. I want to increase my speed so I press the gas, and the vent system locks up and blows air on the windshield and changes to recirc. If I leave all these conditions in place (same speed and throttle position) EXCEPT that I downshift out of OD and force the engine to jump up to 3000 RPM, the system returns to whatever the previous settings were.

At city speeds, I have the same problem, the vent system cuts in and out (does what I have it set for, or what it wants to do) as I go through normal changes in the throttle to maintain reasonable flow with traffic.

I don't know what happens at WOT, but my complaints are that under heavy load and moderate throttle, the vent system does not work as I would want. Under heavy throttle (high engine speeds) the system seems to do what I want it to do.

I get about 16mpg on the freeway, and about 13mpg in mixed driving (over an entire tank of gas), and I carry several hundred pounds of equipment, so the fuel consumption seems about normal. Except for the issues with the ventilation system, I'd have no reason to suspect there is a vacuum leak in my truck. So, whatever is the issue, it does not seem to affect engine operations.

I've got the 4.6L Triton motor, if anybody cares.

I have found this to be the problem several times on Crown Vic's, F150 and Bronco's. The tube looks just fine. If you disconnect and plug it it inside and apply vacuum to the motor end, it will not maintain vacuum because of the tube porosity even though it looks to be in good condition. Sometimes, you can use water in your hand to submerge the line and watch it suck in the water- just be careful to have it disconnected so water doesn't enter the system.

The thing to keep in mind is that the system is rather small and the vacuum cannister is under the hood. Whether for the engine or the cannister, the rate of replenishment to the control valves from the cannister is not as great as the rate of loss thru the porous tube. You can test this by disconnecting the tube from the vacuum motor even with a good tube.

I am only offering this as a good possibility since I went to the trouble of opening up the dash a couple of times before trying this as a quick fix. There is nowhere in the Ford Vacuum Troubleshooting Guide that mentions this as a possobility even though it is quite common in older Ford's. As I understand, the white tube material is the most susceptible for damage when exposed to high heat or UV. Some if not most other colors of the tubing are less problematic. If this is so, I would not understand why Ford continues to use it on that circuit after all these years.

The WOT's I have encountered on the Fords does nothing other than cut out the compressor during heavy acceleration to protect the compressor and make the compressor drive HP available. It has no effect in the cabin other than a slight rise in outlet temp if the cutout condition last a while. I had this happen frequently on my Sable. Elevated temp during cutout was corrected by bringing refrigerant back up to specs.

Lugnut

Jeff, everything you've said about this points to a loss of vacuum somewhere. A hose or plastic line with a hole in it, a vacuum cannister with a small hole. Something like that. Not a completely broken line that would be easy to find, because then the air would stay in the Def mode. Not sure on your year if the vac. cannister is a plastic ball or a black coffee can looking thing, but I know those coffee can type cannisters were good for leaking back in the day.

I wasn't thinking of the charcoal canister because it would throw a P-Code for an Evaporative Emission Control System issue -- P0440, or somewhere in that series.

I was actually hoping somebody would say, it is the hydroflux valve mounted on the framis bracket, it has three wires and the purple hose going to it, you can find it behind the glovebox next to the whatsit container with the thingamabobs in it.

I've searched high and low for actual lines to be broken, loose, disconnected, and so on. Strangly, I can't find any vac hoses other than the fat hose that goes to the brake booster, and two or three others. Whatever I can't find that is the problem, must live under the windshield where the Impossible Spark Plug lives -- the one that almost requires the engine to be dropped to get at. If the vac leak is back there, I'm gonna have a hard time to find it.